Many agricultural tools used for soil tillage, planting and other purposes perform some type of working action on a farm field to change the state of the farm field. For example, soil tillage tools often use one or more rotary coulter discs that enter the soil to a desired depth to break up or till the soil to make the soil ready for planting. A large number of such soil tillage tools are usually mounted on an elongated, laterally extending tool bar that is coupled to the back of a tractor. This allows the soil to be tilled in a large swath behind the tractor as the tool bar and the soil tillage tools carried thereon are towed across a farm field by the tractor. The swath of tilled soil may be basically continuous across its width in a conventional tillage operation or may be separated by strips of untilled soil in a zone tillage operation depending upon the lateral spacing of the soil tillage tools relative to each other on the tool bar.
In some cases, soil tillage tools of the type described above are incorporated into a dedicated, single use tool whose only purpose is to break up or till the soil. After the soil is so tilled and when the farm field is ready for planting, the farmer will then use a separate planter tool to plant seeds into the tilled soil and to cover the planted seeds with soil. However, in other cases, the soil tillage tools may be incorporated into a planter unit such that the soil tillage and planting operations occur essentially at the same time. Regardless of whether the soil tillage and planting operations occur in a two step operation or in a single step operation, it is important that the tool act on or enter into the soil allow the soil to be properly tilled and/or the seeds to be properly planted at the right depth. In accomplishing this goal, most agricultural tools have some type of downpressure system that causes such tools to enter the soil to the proper depth and that attempts to retain the tools at such depth.
The aforementioned downpressure systems can be quite complex and expensive. Some of these systems use multiple mechanical springs or at least one bellows type air bag on each of the soil tillage tools in an attempt to provide sufficient downpressure. Such springs and air bags are exposed to the elements and can in certain situations become caked or fouled with dirt or debris from use, thereby decreasing their effectiveness in supplying the precise amount of downpressure required on the tools. This may result in some tools being located at the proper depth while other tools on the same tool bar are not at the proper depth.
In addition, variations in the soil compaction in the farm field can cause the amount of downpressure required on the tools to vary widely across the length of the tool bar or from one location to another in the farm field. Many downpressure systems known in the prior art are not able to adequately respond to such variations with the result again being that some tools may not be effectively maintained at the required depth. Thus, it would be an advance in the art to provide a downpressure system that is simple and inexpensive in nature, that is durable and is not prone to being fouled during use, and that effectively responds in a real time manner to changes in the downpressure that is required to thereby substantially continuously maintain the tools at the required predetermined depth.